All lessons › Challenge: Food web detectives › Lesson 2
Australian primary science · Years 5–6 (challenge) · Lesson 2 of 3
Why are there so few eagles?
Inquiry question: What happens to energy and matter as they move through a food web?
Marked no materials needed
Pattern seeking
What students learn
Energy enters food webs from the Sun and flows one way: at each step most of it is used for living or lost as heat, so less is passed on. Matter (the atoms that make up living things) is recycled by decomposers.
Success criteria
- I can describe the pattern in the energy data.
- I can explain why there are fewer animals at the top of a food chain.
- I can explain the difference between how energy and matter move in a food web.
Preparation and materials
Before this lesson: Students can read a food web and predict ripple effects (lesson 1).
- iPads with Bottlebrush Education open (nothing else needed) — 13 (one per pair)
- Projector or big screen — 1
Teacher setup
- Open Think like a scientist › Lab › Data detective on your screen to demonstrate.
- Check the iPads are charged and set to Your year › Years 5–6.
Safety and adaptations
Follow school science and equipment risk assessment procedures for the materials used.
Review your school policies and curriculum requirements before teaching.
How to investigate
The lesson sequence should leave pupils with evidence to interpret, not only an activity to finish.
- Pairs study the energy table and describe the pattern in one sentence.
- Calculate: what fraction of the energy passes from each level to the next?
- Predict: how much energy would reach a fifth level? Is a fifth predator likely?
- Open Data detective and solve one data set, to practise spotting patterns and odd results.
- Draw an energy flow arrow diagram and a separate matter cycle diagram showing the decomposers.
Teacher modelling prompt
Show the data table on the big screen. Think aloud: “Grass stores 10 000 units of energy. Grasshoppers only get 1000 of those. So what happened to the other 9000? The grass used some to live, and some was never eaten. Then the grasshoppers use most of their 1000 to hop, grow and stay alive, so the lizards only get 100.” Write 10 000 → 1000 → 100 → 10 on the board and ask: what do you notice?
Record and explain evidence
Recording question: What happens to energy and matter as they move through a food web?
| Level | Example living thing | Energy (units) | What fraction is passed on? | Where did the rest go? |
|---|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Use the table to decide: if energy were recycled, would we need the Sun?
Provided example or reference data
Model data: energy stored in each level of a bush food chain, per square metre per year (rounded)
| Level | Example | Energy stored (units) | Number of living things (example) |
|---|---|---|---|
| 1 Producers | Grass | 10 000 | millions of grass plants |
| 2 Plant eaters | Grasshoppers | 1 000 | thousands |
| 3 Small meat eaters | Blue-tongue lizards | 100 | dozens |
| 4 Top predators | Wedge-tailed eagles | 10 | a few |
Check the data source in the teacher lesson. Illustrative or fictional data are not measurements collected by your class.
Check understanding
What should pupils know? Describe the difference between how energy and matter move through a food web.
Explain with evidence: Use the data to explain why there are far fewer eagles than grasshoppers.
Apply the idea: A farmer can feed more people per paddock by growing wheat for bread than by feeding the wheat to cattle for beef. Use energy flow to explain why.
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.